Determination in vivo of dermal elasticity is complicated by morphological challenges such as subdermal fat and connective tissue. Analytical challenges also exist due to the viscoelastic nature of skin. Several devices are known to be useful in the analysis of physical properties of the skin. For example, a Cutometer device is frequently used for this purpose. However, the viscoelastic property of skin may not allow accurate measurements of dermal elasticity as measured by current, generally recommended Cutometer operation.
The Cutometer software is set to calculate overall elasticity, pure elasticity and a viscoelastic ratio based on linear parameters of the curve. During analysis of a person's skin, vacuum (a negative pressure) is applied to the skin for a short period of time (one second for instance) to achieve an extension of the skin. The vacuum is then released and the skin begins to recover from the deformation during the subsequent period of time known as relaxation. A curve, similar to FIG. 1, is plotted and depicts a deformation distance of the skin in millimeters (mm) along the vertical axis versus time, in seconds, along the horizontal axis.
According to current convention, overall elasticity is calculated by dividing Ua by Uf (Ua/Uf) where Ua is a linear measurement from a level maximum deformation that occurs in the extension curve to a level of recovery by the end of the relaxation or recovery curve. Uf is the maximum deformation of the skin that occurs during the analysis.
Pure elasticity is calculated by dividing Ur by Ue (Ur/Ue) where Ur is the steepest slope on the recovery side as determined by the Cutometer setting. In current practice, Cutometers are recommended by the manufacturer to measure Ur between 1 and 1.1 seconds. Ue is early deformation in the skin generally believed to correlate with the skin elasticity. According to Hooke's law of elasticity, Ue is directionally proportional to the negative pressure applied, which indicates the flexibility of the skin.
The viscoelastic ratio is calculated by dividing Uv by Ue (Uv/Ue), where Uv is Uf minus Ue.
Limitations of relying on the linear parameters as an indication of elasticity are twofold. First, there is an inaccurate description of the elastic properties of the skin. The second drawback is that viscous properties of the skin are also miscalculated. Toward a remedy to these drawbacks, the methods described herein identify an actual inflection point rather than rely on a set infection point identified by the software associated with the measurement device and use an area defined by the curve rather than a linear measurement of the curve to calculate skin properties.